Single speed electric powertrains in battery electric and hybrid electric vehicles pose issues when trying to determine vehicle road-loads on the track as well as the subsequent coast-down road-load determination on a chassis dynamometer due to the fact that these single speed devices often have no true neutral separation of the driveline from the vehicle motion. Therefore, the electric machines and the large rotating inertia and electrical losses therein affect the determination of true road loads, e.g., aerodynamics and rolling resistance, which is determined by time-based coasting of the vehicle from a high speed to a low speed. A proper torque profile of a vehicle coast down from 70 mph to 10 mph in neutral should appear smooth, with no torque fluctuations throughout.
Performing a proper torque profile for a coast-down determination on a hybrid electric transmission vehicle may require a road-load determination procedure that includes turning the vehicle power off (i.e., ignition off) so that no power is being supplied to the electric machine(s). The “powerless” vehicle with no power to the vehicle computing system may be placed in neutral and pushed up to 75 MPH using another vehicle. Once at a high speed steady state, the other vehicle may allow the powerless vehicle to coast down to a low speed state as per the road-load determination procedure. This procedure produces a repeatable and smooth torque response from the wheels that best mimics the natural vehicle road-load data. However, this procedure must be repeated several times to complete the test which requires additional resources including another vehicle to push the powerless test hybrid vehicle. The powerless test hybrid vehicle may disable driver assist systems and/or subsystems, which may result in an undesirable driving experience during the road-load determination procedure.